In gas phase polymerization, a gaseous stream containing one or more monomers is passed through a fluidized bed under reactive conditions in the presence of a catalyst. A polymer product is withdrawn from the reactor, fresh monomer is introduced to the reactor to replace the removed polymer product, and any unreacted monomer is recycled back to the reactor. Process upsets in the reactor are often related to the accumulation or buildup of catalyst and/or polymer particles (“particle accumulation”) on the walls and/or other surfaces, e.g., distribution plate, within the reactor. Particle accumulation is often referred to as sheeting, chunking, drooling, or plugging. When particle accumulation becomes sufficiently large, fluidization can be disrupted, which can require the reactor to be shut down.
Numerous techniques are used to measure the amount of particle accumulation and/or estimate the likelihood that particle accumulation may occur within the reactor. One approach involves measuring the static charge on the catalyst/polymer being produced within the reactor. The principal cause for static charge generation in the reactor is frictional contact of dissimilar materials by a physical process known as frictional electrification or the triboelectric effect. In gas phase polymerization reactors, the static is generated by frictional contact between the catalyst and polymer particles and the reactor walls. The observance of static charge, however, does not necessarily and frequently does not correspond to particle accumulation also occurring within the reactor and in particular catalyst particle accumulation. Conventional static charge measurement systems cannot distinguish between static charge present when particle accumulation is occurring and static charge present when particle accumulation is not occurring.
There is a need, therefore, for improved systems and methods for measuring particle accumulation of catalyst and/or polymer particles within a polymerization reactor.